This invention relates to a process and apparatus for preheating coking coal. The invention involves an improvement over the invention of U.S. Pat. No. 4,102,635 issued Apr. 24, 1978.
The drying and preheating of coking coal is usually effected in an one-stage or two-stage flash drying system. For drying the coal, for instance by heating to a temperature of about 90.degree. C. a one-stage flash dryer is usually sufficient. For a heating to higher temperatures, for instance to about 250.degree. C. a two-stage pipe system is usually used in which in a first stage the drying of the coal is effected to a residual moisture contents of 1 to 2% at a temperature of about 85.degree. to 90.degree. C. The released water vapor in this stage is withdrawn from the pipe system. The subsequent further heating of the mass is effected in a second series connected pipe.
A one-stage single flash drying pipe has also been used in which the recycled moist gases in mixture with hot combustion gases lift the coal which is introduced at the lower end of the flash drying pipe upwards in the pipe. The wast gases leaving the flash drying pipe at the upper end, however, have only a temperature between about 100.degree. and 150.degree. C. (German accepted application No. 1,160,823).
Two-stage flash drying systems are usually operated with two separate pipes which operate in countercurrent insofar as the heat conduct is concerned while a cocurrent exists in the pipe itself. In this case, also, the vapors discharged from the first stage have only a temperature between about 100.degree. and 150.degree. C.
The attempt has also been made to effect the entire preheating of the coking coal to a temperature of about 250.degree. C. in a single flash drying pipe system. In this case, however, in order to reach the desired temperature the entry temperature of the carrier gas had been very high so that through the spontaneous water evaporation from the moist coking coal a large part of the granular mass burst and in which also alteration of the product occurred which resulted in highly undesirable effects on the coking quality of coal.
In the earlier U.S. Pat. No. 4,102,635 these shortcomings were avoided by preheating the coking coal to temperatures between about 180.degree. and 250.degree. C., preferably to about 150.degree. to 180.degree. C. in a single flash drying. In this pipe after preheating the coal in the lower area of the pipe to about 80.degree. to 100.degree. C. a hot combustion gas was introduced at about the midpoint of the flue which gas was at a temperature between 1200.degree. to 1700.degree. C., preferably between about 1400.degree. and 1600.degree. C. Thus, the coal in the second stage was heated to about 120.degree. to 250.degree. C., preferably to 150.degree. to 180.degree. C. This accordingly was a two-stage single pipe flash drying pipe which was operated in cocurrent. A bursting and oxidation of the coal in this process was avoided.
The present invention has the object of improving on the process of the just-described patented invention.